Method of controlling superheat



Jim. 21, 1958 1. v ANDREWS ETAL 2,820,438

METHOD OF CONTROLLING SUPERHEAT Original Filed Dec. 1, 1948 IN Vi N 70R:L V )Q/VDAEWS OLL/SOA/ UAW/G H T ORNE'Y 1 United States Patent 2,820,438METHOD br CONTROLLING SUPERHEAT L V Andrews and Ollison Craig,Worcester, Mass, as-

signors to Riley Stoker Corporation, Worcester, Mass., a corporation ofMassachusetts Original application December 1, 1948, Serial No. 62,854,

now Patent No. 2,679,833, dated June 1, 1954. Divided and thisapplication October 19, 1953, Serial No. 387,012

2 Claims. (Cl. 122-479) This invention relates to the generation andsuperheating of vapor by burning combustible gas, and more particularlyto a method whereby the temperature of superheated vapor may beaccurately controlled despite wide variations in the rate of vaporgeneration.

This application is a division of patent application Serial Number62,854, filed December 1, 1948, now Patent No. 2,679,833.

When steam is to be used for power purposes, it is the common practiceto employ a steam boiler and an assothat the temperature of the steamleaving the superheater will vary with changes in the steam output. Thisis undesirable, and many attempts have been made to maintain asubstantially constant steam temperature, but

the prior arrangements have been subject to various disadvantages. Insome cases dampers are required to control the flow of hot gases, but itis difficult to provide dampers which will close tightly when necessaryand which will withstand the severe operating conditions. Injection ofwater into the steam is a known practice, but unless the water isdistilled it will contaminate the steam. Desuperheaters of the indirectcontact type are expensive and often require complicated piping.

It is accordingly one object of the invention to provide a comparativelysimple, inexpensive, and dependable method for generating andsuperheating vapor to a predetermined temperature by burning combustiblegas.

It is a further object of the invention to provide a novel method forcontrolling the temperature of superheated vapor, such as to avoid thedisadvantages of the prior art.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the steps of the method setforth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention,and in which like reference numerals indicate like parts,

Fig. l is a vertical section through a gas burner and a portion of anassociated furnace wall; and

Fig. 2 is a vertical longitudinal section through a steam generating andsuperheating unit, with the burner of Fig. 1 mounted in operativeposition thereon.

The embodiment illustrated comprises a furnace or combustion chamber 10having a front wall 11, a rear wall 12, and two opposed side walls 14(one only being shown). A horizontal water drum 15 is located adjacentthe top of the rear wall 12, and a small horizontal ,water drum orheader 16 is located adjacent the top Di e .fIQ W811 6 ontalsteam-and-water drum "ice 18 is mounted above the rear water drum 15 andis connected thereto by a bank of upright water tubes 19. Two rows ofwater tubes 20 extend upwardly from the front portion of the water drum15 and then forwardly to the drum 16. A row of water tubes 22 leadsupwardly and rearwardly from the drum 16 to the drum 18 and serves tosupport a roof 23. A superheater 24 is mounted above the water tubes 20and beneath the roof 23, the rear ends of the superheater tubes beingconnected to the drum 18 to receive steam therefrom, and their frontends being connected to a steam outlet header 25. A baffle 27 extendsupwardly from the drum 15 behind the upright portions of the water tubes20, and a baflle 28 extends downwardly from the drum 18 behind the twofront rows of water tubes 19. A wall 30 is located behind the rearmostrow of water tubes 19. A soot hopper 31 is provided between the bottomof the wall 30 and the water drum 15, and a gas outlet duct 32 isprovided at the top of the wall 30, this duct having a damper 33therein. Rows of water wall tubes 35 and 36 are associated with thefront and rear walls 11 and 12 respectively, and a row of water walltubes 37 is associated with each of the side walls 14. As so fardescribed the steam generating and superheating apparatus is of awell-known construction.

In order to Obtain the heat necessary for operation of the apparatus,combustible gas and air are introduced into the furnace as two elementsfor combustion to mix with one another, thereby producing a flame andhot gaseous products of combustion. Steam is generated in the variouswater tubes, particularly in thetubes which are in position to receiveand absorb heat radiated by the flame, and this lowers the temperatureof the combustion gases. The steam travels through the superheater 24,which is in a position to receive heat from the hot gases mainly byconvection.

For the purpose of controlling the temperature of the superheated steam,we vary the luminosity of the flame and thereby vary the rate at whichheat is radiated therefrom to the surrounding water tubes. In thismanner we are able to alter the temperature of the gases reaching thesuperheater and thus obtain control of the superheated steamtemperature. In order to make possible the required variation in flameluminosity, we preferably direct portions of one of the combustionelements in two separate paths. One of these paths is such as to bringabout a comparatively slow mixing of the elements and a luminous flame.The other path is such as to bring about a comparatively rapid mixing ofthe elements and a non-luminous flame. The flame luminosity iscontrolled by varying the relative rates of flow in the respectivepaths.

Referring now particularly to Fig. 1, it will be seen that the frontwall 11 of the furnace is provided with an opening 40 for the admissionof the fuel and air. .In front of this opening there is mounted a burnerbox 41 forming a plenum chamber to which air is supplied under pressurefrom a suitable source through a duct 42 equipped with the usual dampers43. Air flows rearwardly from the box 41 through an opening 45 in therear wall thereof and thence through the furnace wall opening 40. Thisair stream is preferably caused to spin about the axis of the opening40, in known manner, by means of angularly positioned vanes or louvers46 located within the box 41. A fuel nozzle 48 is axially aligned withthe furnace wall opening 40 in position to discharge a comparativelylarge jet of combustible gas rearwardly therethrough. This gas will mixwith the surrounding air rather slowly, producing a highly luminousflame within the furnace. A conical baffle 49 may be mounted on the rearend of the nozzle to deflect the air stream away from the fuel jet andthus still further delay the mixing. 'If desired, a'few small openings50 may be provided through this balfle. Between the burner box 41 andthe wall 11, and surrounding the wall opening 40, there is mounted a gasring 52 in'the'forrn of a hollow torus -having a series of orifices 53from which comparattve'ly small jets of combustible gas are directedinwardly toward the axis of the ring and at a slight angle rearwardlytoward the furnace. 'Since these gas jets travel inwardly acrossthe airstream which flows through the opening 40, the gas and air will mix veryrapidly, producing a substantially non-'lu'minous'flame within thefurnace.

By controlling the relative proportions of fuel gas delivered to thecentral nozzle 48 and to the ring 52 we are able to vary the luminosityof'theflame and thereby control the temperature of the superheatedsteam. Various forms of apparatus maybe employed for this purpose. Inthe particular embodiment illustrated there is provided a three-wayvalve '55 having a valve member 56 controlled by an operating lever '57.This valve has an inlet 59 which is supplied with'fuel gas by a pipe 60,an outlet '62 which is connected to the gas ring 52 by a pipe 63, and anoutlet 65 which is connected to the central nozzle 48 by a pipe '66. Inorder to provide automatic control for the v'alve'56 there is shown apower relay '68 of a suitable and well-known type having an arm 69connected to'the' valvelilever57 by alink 70. A temperature responsivebulb 72is mounted within the superheater outlet headerZ S and connectedto the relay 68' by a small tube 73. This bulb may' be of a known typecontaining a volatile liquid which will vary the fluid pressure at therelay '68 if any variation occurs in the steam temperature.

The operation of the invention will now be apparent from the abovedisclosure. such as natural gas, will be delivered through the pipe 60to the three-way valve '55 at a rate required by the current demand forsteam. Some of this gas will flow through the pipe 63 to the gas ring 52and be discharged from the orifices 53. The remainder of the gas willflow through the pipe "66 and'be dischargedfrom the nozzle 48. Air fromthe duct 42 will flow past the dampers 43 and the louvers 46 to theopening 45 and thence through the wall opening 40, mixing with the gasto produce a flame and hot gaseous products of combustion in the furnace10. These hot gases will travel upwardly past the tubes 20 into contactwith the superheater 24, down wardly behind the baffle 27, and upwardlybehind the baflle 28 to the outlet duct 32. Steam will be genera-ted inthe various heat-exposed water tubes and released in the drum 18, whenceit will travel through the superheater 24 to the header 25. If thetemperature of the steam in this header increased above a desired value,the bulb 72 will increase the fluid pressure transmitted through thetube 73 to the relay 68, which will respond by lowering the arm 69andthe valve lever 57. This will turn the valve member 56 in acounterclockwise direction to cause a greater proportion of the fuel gasto flow through the central nozzle 48, thereby increasing the luminosityof the flame. This will increase the radiation of heat from the flame tothe water tubes surrounding the furnace and thus reduce the temperatureof the 110! gases reaching the superheater, so that less heat will betransmitted by convection to the steam and its temperature will belowered. Similarly, if the steam temperature drops appreciably below thedesired value, the bulb 72 will decrease the fluid pressure transmittedthrough the tube 73 to the relay 68. Consequently the relay arm 69 willmove upwardly, lifting the valve lever 57 and turning the valve member56 in a clockwise direction. This will increase the proportion of thefuel gas flowing through the gas ring 52, and decrease the luminosity ofthe flame. Hence less heat --will be radiated from theflametothe-surroundingwatertubes, the temperatureof A suitablecombustible gas,

the-hotg'ases-reaching thesuperheater will be increase more heat will betransmitted by convection to the steam and the temperature of the steamwill be raised. In th: manner, the steam temperature may be accuratelycor trolled.

Itwill be recognized that the invention provides highly advantageousmethod for controlling the tempera ture of superheated vapor in vaporgenerators fired b gas. The apparatus which may be used is comparativelsimple and inexpensive. If desired, the relay 68 may b omitted, and thevalve lever 57 may then be controllet manually. Any movement of thislever, Whether pro duced automatically or manually, will effect a ver;prompt adjustment of the vapor temperature.

Having thus described our invention, what we clain as new and desire tosecure by Letters Patent is:

1. The method of controlling the temperature of vapor from a superheaterwhich receives its heat mainly by convection from hot gases leaving afurnace, compris ing the steps of introducing the substances of acombustible gas and air into the furnace at closely adjacen' points, oneof such substances being introduced as twc portions forcombustion toproduce a flame, directing one of the said portions in a first path,directing the other of said substances in a second path which surroundsand is parallel to the's'aid first-path to bring about relatively slowmixing of the substancesto render the flame compar'atively luminous, anddirecting the other portion of the saidone of said substances in a pathwhich is directed toward the other of the said substances at asubstantial angle to bring about-relatively rapid-mixing of thesubstances to render the flame comparatively non-luminous, absorbingheat radiated by the flame out of the presence of the superheater; andchanging the relative rates of flow in the said portions to increase anddecrease the luminosity of the flame and the resultant rate of heatradiation therefrom as the vapor temperature increases or decreases,respectively, to thereby decrease or increase, respectively, thetemperature of the hot gases reaching the superheater to maintain thevapor temperatures at a substantially fixed value.

2. The method of producing a superheater vapor at a desired temperature,comprising the steps of supplying a combustible gas and air at closelyadjacent points as two substances for combustion to produce a flame andgaseous products of combustion, directing portions of one of suchsubstances in two separate paths, one path being parallel to thedirection of 'flow of the-other of the said substances to bring aboutrelatively slow mixing of the substances to render the flamecomparatively luminous, the other path surrounding the-said firstpath-and being directed toward and at a substantial-angle to thedirection of flow of the other of the said substances to bringabout-relatively rapid mixingof-the-substances t'o-r'ender the flamecompara tively nonluminous, utilizing heat radiating from the flame toboil liquid and thereby produce vapor, transferring heat mainly byconvection from the said gaseous products to the vapor to superheat thevapor, and changing the relative rates of flow in the said two paths toincrease and decrease the luminosity of the flame and the resultant rateof heat radiation therefrom as the vapor temperature increases ordecreases, respectively, to thereby decrease or increase, respectively,the temperature of the said gaseous products to maintain the vaportemperature at a preselected value.

References Cited in the file of this patent 'UNITED STATES PATENTS

